/Engine/Source/Runtime/Engine/Classes/Engine/EngineTypes.h
Directional light settings for Lightmass
struct FLightmassDirectionalLightSettings : public [FLightmassLightSettings](API\Runtime\Engine\Engine\FLightmassLightSettings)
float
LightSourceAngle
Angle that the directional light's emissive surface extends relative to a receiver, affects penumbra sizes.